Unequal data distribution among different classes usually cause a class imbalance problem. Due to the class imbalance, the classification models become biased toward the majority class and misclassify the minority class. Class imbalance issue becomes more complex when it occurs in multi-class data. The most common method to handle the class imbalance is data resampling that involves either over-sampling minority class instances or under-sampling majority class instances. In the case of under-sampling, there is a chance of losing some crucial information, whereas over-sampling can cause an overfitting problem. Therefore, we propose a novel Cluster-based Hybrid Sampling for Imbalance Data (CBHSID) strategy to address these issues. We calculate the mean of the data observations based on the number of classes. CBHSID uses the calculated mean as a threshold value to segregate majority and minority classes. We apply affinity propagation cluster analysis to each class to create sub-clusters. We calculate the distance of each data item of sub-cluster using centroid mean. We remove data observations that are away from the center of sub-cluster during under-sampling. On the other hand, during the over-sampling, we generate synthetic samples using data observations near to the center of sub-cluster. We compared our proposed approach with a few state-of-the-art data balancing methods on 12 binary and 4 multi-class benchmark datasets. Based on Geometric-Mean (G-Mean), Recall, and F1-score, our method outperformed the other compared methods on 14 datasets out of 16. We identified that CBHSID is suitable for addressing class imbalance issues in both binary and multi-class classifications. In the current state, we have only validated CBHSID on stationary data streams. Consequently, CBHSID can further be tested on non-stationary data streams in online learning environments.

The social media networks have evolved rapidly and people frequently use these services to communicate with others and express themselves by sharing opinions, views, ideas etc. on different topics. The social media trend analysis is generally carried out by sifting the corresponding or interlinked events discussed on social media websites such as Twitter, Facebook etc. The fundamental objective behind such analyses is to determine the level of criticality with respect to criticism or appreciation described in the comments, tweets or blogs. The trend analysis techniques can also be systematically exploited for opinion making among the masses at large. The results of such analyses show how people think, assess, orate and opine about different issues. This paper primarily focuses on the trend detection and sentiment analysis techniques and their efficacy in the contextual information. We further discuss these techniques which are used to analyze the sentiments expressed within a particular sentence, paragraph or document etc. The analysis based on sentiments can pave way for automatic trend analysis, topic recognition and opinion mining etc. Furthermore, we can fairly estimate the degree of positivity and negativity of the opinions and sentiments based on the content obtained from a particular social media.

In real-time streaming data, concept drift and class imbalance may occur simultaneously which causes the performance degradation of the online machine learning models. Most of the existing work is limited to addressing these issues for binary class data streams. Very little focus is given to the multi-class data streams. The most common approach to address these issues is ensemble learning. Ensemble learning consists of multiple classifiers combined which are trained on different subsets of the data to improve the overall accuracy. The performance of the ensemble learning approach suffers in case the new classifier is not trained on appropriate data (the data about the new concept). To address this gap, this study has proposed a Smart Adaptive Ensemble Model (SAEM) to address the issues of concept drift and class imbalance for multi-class data streams. The SAEM monitors the feature-level change in data distribution and creates a background ensemble to train the new classifier on features that observe change. To address the class imbalance issue, SAEM applies higher weights on the minority class instances using the dynamic class imbalance ratio. The proposed model outperformed the existing state-of-the-art approaches on the eight different data streams. The results showed an average improvement of 15.857% in accuracy, 20.35% in Kappa, 16.12% in F1-score, 15.58% in precision, and 16.42% in recall. The Friedman test confirmed statistically significant performance differences among all models across five key metrics. Based on the obtained results, the research findings strongly support the notion that SAEM exhibits enhanced effectiveness and efficiency as a solution for online learning applications.